This document describes how to cross compile Erlang/OTP-R14B02. Note that
the support for cross compiling Erlang/OTP should be considered as
experimental. As far as we know, the R14B02 release should cross compile
fine, but since we currently have a very limited set of cross compilation
environments to test with we cannot be sure. The cross compilation support
will remain in an experimental state until we get a lot more cross compilation
environments to test with.

You are advised to read the whole document before attempting to cross
compile Erlang/OTP. However, before reading this document, you should read
the $ERL_TOP/INSTALL.md document which describes building and installing
Erlang/OTP in general. $ERL_TOP is the top directory in the source tree.

otp_build Versus configure/make

Building Erlang/OTP can be done either by using the $ERL_TOP/otp_build
script, or by invoking $ERL_TOP/configure and make directly. Building using
otp_build is easier since it involves fewer steps, but the otp_build build
procedure is not as flexible as the configure/make build procedure. Note
that otp_build configure will produce a default configuration that differs
from what configure will produce by default. For example, currently
--disable-dynamic-ssl-lib is added to the configure command line arguments
unless --enable-dynamic-ssl-lib has been explicitly passed. The binary
releases that we deliver are built using otp_build. The defaults used by
otp_build configure may change at any time without prior notice.

Cross Configuration

The $ERL_TOP/xcomp/erl-xcomp.conf.template file contains all available cross
configuration variables and can be used as a template when creating a cross
compilation configuration. All cross configuration variables are also
listed at the end of this document. For examples of working cross
configurations see the $ERL_TOP/xcomp/erl-xcomp-TileraMDE2.0-tilepro.conf
file and the $ERL_TOP/xcomp/erl-xcomp-x86_64-saf-linux-gnu.conf file. If the
default behavior of a variable is satisfactory, the variable does not need to
be set. However, the configure script will issue a warning when a default
value is used. When a variable has been set, no warning will be issued.

A cross configuration file can be passed to otp_build configure using the
--xcomp-conf command line argument. Note that configure does not accept
this command line argument. When using the configure script directly, pass
the configuration variables as arguments to configure using a
<VARIABLE>=<VALUE> syntax. Variables can also be passed as environment
variables to configure. However, if you pass the configuration in the
environment, make sure to unset all of these environment variables before
invoking make; otherwise, the environment variables might set make variables
in some applications, or parts of some applications, and you may end up with
an erroneously configured build.

What can be Cross Compiled?

All Erlang/OTP applications except the wx application can be cross compiled.
The build of the wx driver will currently be automatically disabled when
cross compiling.

Compatibility

The build system, including cross compilation configuration variables used,
may be subject to non backward compatible changes without prior notice.
Current cross build system has been tested when cross compiling some Linux/GNU
systems, but has only been partly tested for more esoteric platforms. The
VxWorks example file is highly dependent on our environment and is here more
or less only for internal use.

Patches

Please submit any patches for cross compiling in a way consistent with this
system. All input is welcome as we have a very limited set of cross compiling
environments to test with. If a new configuration variable is needed, add it
to $ERL_TOP/xcomp/erl-xcomp.conf.template, and use it in configure.in.
Other files that might need to be updated are:

$ERL_TOP/xcomp/erl-xcomp-vars.sh

$ERL_TOP/erl-build-tool-vars.sh

$ERL_TOP/erts/aclocal.m4

$ERL_TOP/xcomp/README.md

$ERL_TOP/xcomp/erl-xcomp-*.conf

Note that this might be an incomplete list of files that need to be updated.

We will first go through the configure/make build procedure which people
probably are most familiar with.

Building With configure/make Directly

(1)

Change directory into the top directory of the Erlang/OTP source tree.

$ cd $ERL_TOP

In order to compile Erlang code, a small Erlang bootstrap system has to be
built, or an Erlang/OTP system of the same release as the one being built
has to be provided in the $PATH. The Erlang/OTP for the target system will
be built using this Erlang system, together with the cross compilation tools
provided.

If you want to build the documentation out of the same source tree as you are
cross compiling in, you currently need a full Erlang/OTP system of the same
release as the one being built for the build machine. If this is the case,
build and install one for the build machine (or use one already built) and add
it to the $PATH before cross building, and building the documentation. See
the How to Build the Documentation section in the $ERL_TOP/INSTALL.md
document for information on how to build the documentation.

If you want to build using a compatible Erlang/OTP system in the $PATH,
jump to (3).

Building a Bootstrap System

(2)

$ ./configure --enable-bootstrap-only
$ make

The --enable-bootstrap-only argument to configure isn't strictly necessary,
but will speed things up. It will only run configure in applications
necessary for the bootstrap, and will disable a lot of things not needed by
the bootstrap system. If you run configure without --enable-boostrap-only
you also have to run make as make bootstrap; otherwise, the whole system will
be built.

<HOST> is the host/target system that you build for. It does not have to be
a full CPU-VENDOR-OS triplet, but can be. The full CPU-VENDOR-OS triplet
will be created by executing $ERL_TOP/erts/autoconf/config.sub <HOST>. If
config.sub fails, you need to be more specific.

<BUILD> should equal the CPU-VENDOR-OS triplet of the system that you
build on. If you execute $ERL_TOP/erts/autoconf/config.guess, it will in
most cases print the triplet you want to use for this.

Pass the cross compilation variables as command line arguments to configure
using a <VARIABLE>=<VALUE> syntax.

Note

You can not pass a configuration file using the --xcomp-conf
argument when you invoke configure directly. The --xcomp-conf argument
can only be passed to otp_build configure.

make will verify that the Erlang/OTP system used when building is of the
same release as the system being built, and will fail if this is not the case.
It is possible, however not recommended, to force the cross compilation even
though the wrong Erlang/OTP system is used. This by invoking make like this:
make ERL_XCOMP_FORCE_DIFFERENT_OTP=yes.

You can either install using the installation paths determined by configure
(4), or install manually using (5).

Installing Using Paths Determined by configure

(4)

$ make install DESTDIR=<TEMPORARY_PREFIX>

make install will install at a location specified when doing configure.
configure arguments specifying where the installation should reside are for
example: --prefix, --exec-prefix, --libdir, --bindir, etc. By default
it will install under /usr/local. You typically do not want to install your
cross build under /usr/local on your build machine. Using DESTDIR
will cause the installation paths to be prefixed by $DESTDIR. This makes it
possible to install and package the installation on the build machine without
having to place the installation in the same directory on the build machine as
it should be executed from on the target machine.

When make install has finished, change directory into $DESTDIR, package
the system, move it to the target machine, and unpack it. Note that the
installation will only be working on the target machine at the location
determined by configure.

Installing Manually

(5)

$ make release RELEASE_ROOT=<RELEASE_DIR>

make release will copy what you have built for the target machine to
<RELEASE_DIR>. The Install script will not be run. The content of
<RELEASE_DIR> is what by default ends up in /usr/local/lib/erlang.

The Install script used when installing Erlang/OTP requires common Unix
tools such as sed to be present in your $PATH. If your target system
does not have such tools, you need to run the Install script on your
build machine before packaging Erlang/OTP. The Install script should
currently be invoked as follows in the directory where it resides
(the top directory):

$ ./Install [-cross] [-minimal|-sasl] <ERL_ROOT>

where:

-minimal Creates an installation that starts up a minimal amount
of applications, i.e., only kernel and stdlib are started. The
minimal system is normally enough, and is what make install uses.

-sasl Creates an installation that also starts up the sasl
application.

-cross For cross compilation. Informs the install script that it
is run on the build machine.

<ERL_ROOT> - The absolute path to the Erlang installation to use
at run time. This is often the same as the current working directory,
but does not have to be. It can follow any other path through the file
system to the same directory.

If neither -minimal, nor -sasl is passed as argument you will be
prompted.

You can now either do:

(6)

Decide where the installation should be located on the target machine,
run the Install script on the build machine, and package the installed
installation. The installation just need to be unpacked at the right
location on the target machine:

Building With the otp_build Script

If you have your cross compilation configuration in a file, pass it using the
--xcomp-conf=<FILE> command line argument. If not, pass --host=<HOST>,
--build=<BUILD>, and the configuration variables using a <VARIABLE>=<VALUE>
syntax on the command line (same as in (3)). Note that <HOST> and <BUILD>
have to be passed one way or the other; either by using erl_xcomp_host=<HOST>
and erl_xcomp_build=<BUILD> in the configuration file, or by using the
--host=<HOST>, and --build=<BUILD> command line arguments.

otp_build configure will configure both for the boostrap system on the
build machine and the cross host system.

(10)

$ ./otp_build boot -a

otp_build boot -a will first build a bootstrap system for the build machine
and then do the cross build of the system.

(11)

$ ./otp_build release -a <RELEASE_DIR>

otp_build release -a will do the same as (5), and you will after this have
to do a manual install either by doing (6), or (7).

Note that you cannot define arbitrary variables in a cross compilation
configuration file. Only the ones listed below will be guaranteed to be
visible throughout the whole execution of all configure scripts. Other
variables needs to be defined as arguments to configure or exported in
the environment.

Variables for otp_build Only

Variables in this section are only used, when configuring Erlang/OTP for
cross compilation using $ERL_TOP/otp_build configure.

Note

These variables currently have no effect if you configure using
the configure script directly.

erl_xcomp_build - The build system used. This value will be passed as
--build=$erl_xcomp_build argument to the configure script. It does
not have to be a full CPU-VENDOR-OS triplet, but can be. The full
CPU-VENDOR-OS triplet will be created by
$ERL_TOP/erts/autoconf/config.sub $erl_xcomp_build. If set to guess,
the build system will be guessed using
$ERL_TOP/erts/autoconf/config.guess.

erl_xcomp_host - Cross host/target system to build for. This value will
be passed as --host=$erl_xcomp_host argument to the configure script.
It does not have to be a full CPU-VENDOR-OS triplet, but can be. The
full CPU-VENDOR-OS triplet will be created by
$ERL_TOP/erts/autoconf/config.sub $erl_xcomp_host.

Cross Compiler and Other Tools

If the cross compilation tools are prefixed by <HOST>- you probably do
not need to set these variables (where <HOST> is what has been passed as
--host=<HOST> argument to configure).

All variables in this section can also be used when native compiling.

CC - C compiler.

CFLAGS - C compiler flags.

STATIC_CFLAGS - Static C compiler flags.

CFLAG_RUNTIME_LIBRARY_PATH - This flag should set runtime library
search path for the shared libraries. Note that this actually is a
linker flag, but it needs to be passed via the compiler.

CPP - C pre-processor.

CPPFLAGS - C pre-processor flags.

CXX - C++ compiler.

CXXFLAGS - C++ compiler flags.

LD - Linker.

LDFLAGS - Linker flags.

LIBS - Libraries.

Dynamic Erlang Driver Linking

Note

Either set all or none of the DED_LD* variables.

DED_LD - Linker for Dynamically loaded Erlang Drivers.

DED_LDFLAGS - Linker flags to use with DED_LD.

DED_LD_FLAG_RUNTIME_LIBRARY_PATH - This flag should set runtime library
search path for shared libraries when linking with DED_LD.

Large File Support

Note

Either set all or none of the LFS_* variables.

LFS_CFLAGS - Large file support C compiler flags.

LFS_LDFLAGS - Large file support linker flags.

LFS_LIBS - Large file support libraries.

Other Tools

RANLIB - ranlib archive index tool.

AR - ar archiving tool.

GETCONF - getconf system configuration inspection tool. getconf is
currently used for finding out large file support flags to use, and
on Linux systems for finding out if we have an NPTL thread library or
not.

Cross System Root Locations

erl_xcomp_sysroot - The absolute path to the system root of the cross
compilation environment. Currently, the crypto, odbc, ssh and
ssl applications need the system root. These applications will be
skipped if the system root has not been set. The system root might be
needed for other things too. If this is the case and the system root
has not been set, configure will fail and request you to set it.

erl_xcomp_isysroot - The absolute path to the system root for includes
of the cross compilation environment. If not set, this value defaults
to $erl_xcomp_sysroot, i.e., only set this value if the include system
root path is not the same as the system root path.

Optional Feature, and Bug Tests

These tests cannot (always) be done automatically when cross compiling. You
usually do not need to set these variables.

Warning

Setting these variables wrong may cause hard to detect
runtime errors. If you need to change these values, really make sure
that the values are correct.

Note

Some of these values will override results of tests performed
by configure, and some will not be used until configure is sure that
it cannot figure the result out.

The configure script will issue a warning when a default value is used.
When a variable has been set, no warning will be issued.

erl_xcomp_after_morecore_hook - yes|no. Defaults to no. If yes,
the target system must have a working __after_morecore_hook that can be
used for tracking used malloc() implementations core memory usage.
This is currently only used by unsupported features.

erl_xcomp_bigendian - yes|no. No default. If yes, the target system
must be big endian. If no, little endian. This can often be
automatically detected, but not always. If not automatically detected,
configure will fail unless this variable is set. Since no default
value is used, configure will try to figure this out automatically.

erl_xcomp_clock_gettime_cpu_time - yes|no. Defaults to no. If yes,
the target system must have a working clock_gettime() implementation
that can be used for retrieving process CPU time.

erl_xcomp_getaddrinfo - yes|no. Defaults to no. If yes, the target
system must have a working getaddrinfo() implementation that can
handle both IPv4 and IPv6.

erl_xcomp_gethrvtime_procfs_ioctl - yes|no. Defaults to no. If yes,
the target system must have a working gethrvtime() implementation and
is used with procfs ioctl().

erl_xcomp_dlsym_brk_wrappers - yes|no. Defaults to no. If yes, the
target system must have a working dlsym(RTLD_NEXT, <S>) implementation
that can be used on brk and sbrk symbols used by the malloc()
implementation in use, and by this track the malloc() implementations
core memory usage. This is currently only used by unsupported features.

erl_xcomp_kqueue - yes|no. Defaults to no. If yes, the target
system must have a working kqueue() implementation that returns a file
descriptor which can be used by poll() and/or select(). If no and
the target system has not got epoll() or /dev/poll, the kernel-poll
feature will be disabled.

erl_xcomp_linux_clock_gettime_correction - yes|no. Defaults to yes on
Linux; otherwise, no. If yes, clock_gettime(CLOCK_MONOTONIC, _) on
the target system must work. This variable is recommended to be set to
no on Linux systems with kernel versions less than 2.6.

erl_xcomp_linux_usable_sigaltstack - yes|no. Defaults to yes on Linux;
otherwise, no. If yes, sigaltstack() must be usable on the target
system. sigaltstack() on Linux kernel versions less than 2.4 are
broken.

erl_xcomp_linux_usable_sigusrx - yes|no. Defaults to yes. If yes,
the SIGUSR1 and SIGUSR2 signals must be usable by the ERTS. Old
LinuxThreads thread libraries (Linux kernel versions typically less than
2.2) used these signals and made them unusable by the ERTS.

erl_xcomp_poll - yes|no. Defaults to no on Darwin/MacOSX; otherwise,
yes. If yes, the target system must have a working poll()
implementation that also can handle devices. If no, select() will be
used instead of poll().

erl_xcomp_putenv_copy - yes|no. Defaults to no. If yes, the target
system must have a putenv() implementation that stores a copy of the
key/value pair.

erl_xcomp_reliable_fpe - yes|no. Defaults to no. If yes, the target
system must have reliable floating point exceptions.

The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.

Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.